Field of the Invention
The invention relates to a hydrokinetic coupling of the type having a primary vane wheel and a secondary vane wheel which together define a toroidal working chamber, which can be filled with working fluid via a filling line. A shell rotates with the primary vane wheel and also envelops the secondary vane wheel, and at least one constantly open and throttled outlet port and also an outlet valve are provided in the shell for removing heating generated in the working fluid. The outlet valve can be closed by means of control hydraulic pressure present in a control line but only when there is little slip in the coupling.
Brief Description of the Prior Art
Hydrokinetic couplings of this type are known from German Pat. No. 883 377. In such couplings, a part of the working fluid is continually allowed to flow out of the working chamber into the region outside the coupling for the purpose of removing heat generated in the working fluid. An appropriate quantity of cooled working fluid is continually supplied to the working chamber via a filling line. The heated working fluid flows away via at least one constantly open, throttled outlet aperture disposed in the shell. As the throttled outlet aperture is disposed in the shell, which rotates with the primary vane wheel, i.e. generally always at a uniform rotational speed, only a completely specific amount of fluid can ever flow away through the throttled outlet aperture. However, the amount of heat generated per unit time varies a lot: As long as the hydrokinetic coupling operates in the normal working condition with relatively little slip (on the order of 3%), little heat is generated. However during starting matters are quite different, i.e. when a machine is to be accelerated. In this case the secondary vane wheel is at a stand still at the beginnning, while the primary vane wheel is rotating at full engine speed. This means that in the first moment of starting the slip is 100% and that the entire mechanical energy supplied is converted into heat. Although the secondary rotational speed subsequently increases more or less quickly and the development of heat is consequently less, nevertheless the starting condition is a critical phase which in the short term requires a high rate of flow of working fluid through the coupling so as to remove the heat to the outside. In the normal operating condition, on the other hand, only a small throughput quantity of fluid is required.
Various constructions have become known with which a solution to the following task is found--i.e. the amount of working fluid flowing out of the working chamber is automatically adjusted to the instantaneously generated heat. Thus in the starting condition a large amount of working fluid leaves the working chamber and in the normal operating condition only a small amount of working fluid is allowed to leave it.
German Pat. No. 883,377 provides, apart from the constantly open, throttled outlet port, an additional outlet which is disposed in the shell rotating with the primary vane wheel. This valve is kept closed by means of control fluid pressure; it opens in the absence of this control fluid pressure. The supply of control fluid pressure is regulated by means of a control valve, which is operated as a function of the temperature of the working fluid with the aid of a thermostat. This thermostat control valve is disposed in a stationary housing part. Consequently the control line, originating from the control valve, firstly passes through the stationary housing part and opens into a collecting groove rotating with the shell; from there it passes through the shell to the outer valve. In the embodiment of German Pat. No. 883 377 the working fluid leaving the working chamber flows into a second shell also rotating with the primary vane wheel. From there it is conveyed by means of a scoop pipe--past the previously mentioned thermostat--via a radiator back into the working chamber. However if, according to a preferred embodiment, the working fluid is allowed to spray off into a stationary tank and from there it returns by means of a pump via a radiator into the working chamber, then it is difficult to incorporate the thermostat control valve into the system so that the control fluid pressure is guaranteed to be safely switched on and off in the required way. It is therefore desirable to dispense with this type of thermostat control valve completely.
The hydrokinetic coupling from German Pat. No. 919 449 has a further means for removing a greater amount of working fluid during the starting operation. This means includes at least a scoop pipe disposed on the outside of the secondary vane wheel. This may well increase the amount of fluid flowing out of the working chamber during the first phase of the starting operation. However, the effect of this scoop pipe is considerably weaker with average slip values than with 100% slip. A further disadvantage of such a scoop pipe lies in that it causes a degree of energy loss under normal operating conditions and the coupling does not attain the required minimum slip value, which should be as low as possible.
Theoretically it would still be possible to control the outlet ports, e.g. by means of annular sluice valves as in German Pat. No. 16 00 974. However the expenditure associated with this would be unduly high. Here it should be borne in mind that the coupling according to the invention is preferably intended for applications in which a change in the slip and consequently in the secondary rotational speed is not required during normal operation. In other words, the coupling according to the invention is of the non-controllable type of coupling. Nevertheless it does have the appliances described above to remove the heat generated in the working fluid.
The object of the invention is to develop further a hydrokinetic coupling in accordance with the claims herein, so that the amount of fluid continually flowing out of the working chamber is automatically adjusted to a large value if the slip in the coupling is greater and to a low value if the slip in the coupling is small, without a control valve being required for operating the outlet valve or additional components, such as scoop pipes, for example.